A light source unit of this kind for unipolar operation is known and comprises a U-shaped envelope made from glass tube material and having two parallel legs ending in sockets providing for connecting pins. The known unit can be used for optical presentation of information, i.e., presentation of alpha numeric signs, graphics and pictures displayed on a screen or display, respectively. Such a display consists of a matrix of picture elements, each picture element consisting of a monochrome light signal source in case of a monochrome display. In case of color presentation of information, one picture element is composed of three single light source units of the primary colors red, green and blue forming a so-called pixel. The desired or required, respectively, color impression is then created physiologically by additive mixture of the three primary colors within the human eye/brain system.
Presenting information to a large audience in the open air means looking for a correspondingly large area display which is distinctly visible not only at night but also during day light and with sufficient optical resolution from a greater viewing distance. In case of presentation of rapidly moving pictures, like in television, the picture information changes up to 100 times per second (and up to 120 times per second in the U.S.). At the same time the temperature of the outside environment can fluctuate over a wide range, e.g., -20.degree. to +50.degree. C.
While the known light source unit is able to fulfill the demands stipulated above, there are some drawbacks present:
1. The known light source unit is presenting towards the audience the curved portion of the U-shaped envelope only so that no more than approximately 20% of the radiation is effective. The rest is dissipating, especially through the parallel legs of the U-shaped envelope which are arranged substantially normal or perpendicular, respectively, to the plane of fixation of a unit, said plane being also substantially normal to the viewing direction of the spectators.
2. The production costs are relatively high in view of special workmanship and single manufacture of each unit being necessary, including application of the sockets by hand.